THE FAMILIES AND GENEEA OF BATS. 
15 
teristic of families. In a group like the bats, where divergence from 
ordinary mammals has been chiefly in the direction of changing the 
front limbs from legs to wings, it seems necessary to give special 
weight in classification to such characters as these. 
Pteropidaz . — The very characteristic structure of the humerus in 
this group shows no important variation in the numerous genera 
that I have examined. The head is broadly rounded, slightly oval in 
outline, well defined everywhere, except on the side next the trochiter, 
into which it merges. Trochiter ill-defined, low and broad, scarcely 
rising above base of head, to which it is joined by a level, smoothly 
rounded surface. Trochin slightly higher and narrower than troch- 
iter, and much better defined, a well-developed groove, about as wide 
as its lateral diameter, separating it from head, and a similar though 
even more strongly defined groove isolating it dorsally from the low, 
broad, deltoid crest. Shaft somewhat triangular proximally, flat- 
tened distally, its sigmoid flexure distinct. Capitellum moved out- 
ward slightly beyond line of shaft and entirely obliterating epicon- 
dyle. Epitrochlea large, its lateral diameter more than half that of 
capitellum, its spinous process distinct, though short. 
Microchiroptera .— The least specialized type of humerus in the 
Microchiroptera is found in the Rhinopomidse and Emballonuridse. 
In these families both trochin and trochiter have risen about to level 
of upper surface of head of humerus, a development which causes 
little change in the form of either tubercle as compared with its con- 
dition in the Pteropidse. The alteration in form is most noticeable 
in the trochiter, which is now well defined throughout, and separated 
from head by a distinct groove over which the smooth surface of 
the head is extended. This groove is narrower and better defined 
than that dividing the head from the trochin. Though so distinctly 
increased in size the trochiter is not large enough to reach the edge 
of the glenoid fossa of the scapula, the shoulder joint remaining 
therefore strictly single. Head globular in Rhinopoma , somewhat 
compressed in the Emballonuridse. As in all other Microchiroptera 
the deltoid crest is high and knifelike, very different from the low, 
rounded form in the Megachiroptera. The shaft of the bone is 
nearly terete throughout, except where distorted by the deltoid crest, 
and a little flattened distally. It has a slight single curvature. 
Capitellum essentially as in the Pteropidse. 
A slight modification of this type is^ found in the Noctilionidse. 
Here the head of the humerus is greatly compressed and strikingly 
ridgelike. The well-defined trochiter is very small and narrow, 
though rising fully as high as in the related groups, while the trochin 
is greatly increased in size, being nearly as large as the head. The 
groove separating the trochin from the well-developed though rather 
small deltoid crest is ill-defined. 
